The present invention relates to a photographic binder for forming photographic layers of photographic light sensitive materials. The term "photographic layers" herein used includes silver halide light sensitive layers, protective layers, inter layers, under coat layers, diffusion transfer image receiving layers, etc.
Many attempts have been made to produce photographic light sensitive materials using synthetic resins in place of gelatin as a binder for photographic layers. However, most of the synthetic resins do not solidify and gel even if their solutions are cooled. Thus, with such synthetic resins, it is impossible to form uniform photographic layers by cooling the solution to cause loss of fluidity as in the case of using gelatin. Even if gelatin is used, gelling of the solution is not enough to coat it when gelatin concentration is lower than a certain limit (usually 1%).
A number of vinyl monomers have been known which can copolymerize with maleic anhydride to form alternating copolymers. Examples of these vinyl monomers are olefinic unsaturated compounds such as styrene, vinyl methyl ether, vinyl butyl ether, vinyl acetate, ethylene, isobutylene, etc. Use of these alternating copolymers for production of light sensitive materials is disclosed, e.g., in Japanese Patent Publication No. 4272/64, Japanese Patent Publication No. 22662/69 and Japanese Laid-open Patent Application No. 15123/72.
Example of use of a treated product (called "PVA treated product" hereinafter) obtained by heating such maleic anhydride alternating copolymer together with polyvinyl alcohol as a binder of the photographic layers is disclosed in Japanese Patent Publication No. 22504/71 where a heat modified product of styrene-maleic anhydride copolymer and polyvinyl alcohol is used.
When the PVA treated product obtained by using the styrene-maleic anhydride copolymer disclosed in said Japanese Patent Publication is mixed with a photographic coating liquid having no gelling ability, such coating liquid can be coated on a support and dried in the same manner as in the case of using gelatin as a binder. However, the resultant dried photographic layer is hard and brittle. Therefore, the photographic layer of light sensitive materials which uses such PVA treated product is apt to form cracks or to curl up.